Thermal Degradation and Flame Retardance of Biobased Polylactide Composites Based on Aluminum Hypophosphite

A series of flame retardant polylactide composites (FR-PLA) based on aluminum hypophosphite (AHP) were facilely prepared by melt blending method. The thermal behavior, flammability, and mechanical properties of FR-PLA composites were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), the UL-94 vertical burning test, limiting oxygen index (LOI), cone calorimeter testing, microscale combustion calorimetry, mechanical testing, and dynamic mechanical analysis (DMA). TGA results showed that the FR-PLA composites presented higher char residue and reduced mass loss rate than neat PLA. The FR-PLA composite showed excellent fire resistance, from no rating of neat PLA to a V0 rating of FR-PLA containing 20 wt % aluminum hypophosphite in the UL-94 test. The microscale combustion calorimetry test showed that the heat release capacity, the peak of heat release and the total heat release of FR-PLA composites were significantly decreased with the increase of AHP content. The cone calorimeter test also confirmed that the addition of AHP resulted in a significant decrease in the peak heat release rate value of PLA/AHP composites compared with pure PLA. Additionally, the results from DSC and DMA tests indicated that the addition of AHP into polylactide significantly changed the crystallization behavior and storage modulus of polylactide. However, the addition of AHP decreases the tensile strength and elongation at break. The char after LOI testing was investigated by scanning electron microscopy and craterlike morphology was observed on the surface of the char. The thermal degradation process of FR-PLA composites was analyzed by real-time Fourier transform infrared spectroscopy.